Abstract
ABSTRACTThis work aims to study the effect of degree of protein aggregation on the surface and rheological properties of whey protein isolate dispersions with different concentrations (80, 100 and 120 g/kg), pHs (5.5 or 6.5) or NaCl contents (1 or 2 g/kg). Dispersions were thermally treated at 70, 75 and 80°C for different times. By mixing aggregated with native protein dispersions, different degrees of aggregation (0%, 20%, 40%, 60% and 80%) were obtained. Surface tension of the dispersions was determined by the pendant drop method, whilst their rheological properties were obtained from flow curve tests. A slight effect of the degree of aggregation over diffusion was found, which indicates that native proteins dominated the decrease in surface tension. The rheological behavior of dispersions with NaCl addition changed from Newtonian to shear thinning for aggregation degrees above 20%, whilst all dispersions at pH 5.5 and 6.5 presented a shear thinning behavior.
Highlights
Whey protein isolate (WPI) is one of the highest quality proteins because of their amino acid profile and rapid digestibility (Devries & Phillips, 2015)
In opposition to the results obtained for these authors, in this study, only the second period was observed from the Dynamic surface tension (DST) curves in view of the relatively short measuring times and the relatively high WPI dispersion concentration (8–12 g/kg) used
We determined that the surface tension decreased from 60.5 to 49.2 mN/m for samples with NaCl addition, and from 61.3 to 47.8 mN/m for samples with change in their pH, results in agreement with literature data for WPI dispersions
Summary
Whey protein isolate (WPI) is one of the highest quality proteins because of their amino acid profile and rapid digestibility (Devries & Phillips, 2015). Rapid diffusion of protein molecules to the air–water interface followed by molecular rearrangement allows proteins to decrease the surface tension and stabilize the gas phase (Germain & Aguilera, 2014). It has been demonstrated that surface tension of proteins dispersions correlated to their foaming properties (Mahmoudi, Axelos, & Riaublanc, 2011; Rullier, Novales, & Axelos, 2008; Tamm, Sauer, Scampicchio, & Drusch, 2012). Another key property in foam stabilization is the apparent viscosity of the continuous phase.
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